This proposal focuses on the development of Inhibitory Control (IC) in boys and girls of elementary school age, through assessment by performance tasks. By introducing these tasks into a longitudinal study, The Project on Human Development in Chicago Neighborhoods, and a clinical sample from the The Children's Hospital, Boston, IC will studied longitudinally in 200 males and 200 females beginning when they are 5 to 6 years old. The research aims of this study are: 1) Characterize growth of IC as a function of gender and clinical status for Normal Controls, and for children with CD, ADHD, and co-morbid ADHD-CD; 2) Characterize growth of IC as a function of gender, timing of onset, and pervasiveness of CD; and 3) Characterize growth of IC as a function of gender and parenting practices. Each of the 3 aims will help to identify potential core disturbances in the development of IC that relate to gender, psychopathology, and environmental factors important to child development. These core disturbances may have implications for interventions devoted to altering environmental influences on child development and clinical course of CD. The career development aims of this study are: 1) Enhance my knowledge of conceptual and empirical approaches in cognitive neuroscience, and apply these to the study of growth of IC in children; 2) Enhance my knowledge of environmental influences on child development, in order to examine the role played by these on growth of IC in children; and 3) Become more proficient in conducting multivariate, longitudinal research in order to study developmental risk for psychopathology. At the end of the training period, the candidate expects to have collected three waves of data on the children enrolled in the study. He will be able to select relevant indices from the data, and construct appropriate multivariate statistical models to answer the questions of the research aims. The candidate expects to interpret the findings emerging from the analyses according to current principles of cognitive neuroscience, and he will be able to draw conclusions about the role of gender, psychopathology, and environmental factors in shaping the development of Inhibitory Control.